The present invention pertains in general to slew controls and more particularly to variable rate bi-directional slew controls for digital systems and methods therefor.
Slew controls are useful anywhere that the slewing of digital values to achieve a precise setting over wide ranges is desired. The setting of output values for frequency synthesizers, the setting of precise timing and/or the setting of precise delay in electronic test and measurement equipment, and the control of machine tool equipment are all examples of applications in which a variable rate bi-directional slew control is valuable.
One approach to providing a bi-directional slew control for a digital system involves the use of a keyboard interface in which one buttom is pushed to count up and another button is pushed to count down. However, it is difficult to control the slewing rate when using a push button and it is also difficult to stop instantly at a desired value when using a push button.
In another approach, an operator interface allowing more precise control of slewing rate is achieved by using a knob attached to a circular glass or plastic disk inscribed with marks at intervals about its circumference or to a metal disk with slotted holes at intervals about its circumference. Slew rate is determined by the number of scribed marks or holes that passes through a light beam in a given period of time. This sort of system is, however, costly and difficult to implement. In addition, slew rate is limited by the rate at which the knob can be turned by hand.